Leprosy: histamine test: practice question

A Dermatology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Dermatology · Leprosy: histamine test

Sample item

When intradermal histamine is injected into an anaesthetic leprosy patch, which part of the triple response is absent?

AThe central red spotBThe central whealCAll three components are normalDThe flare, as the axon reflex is lost

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. The flare, as the axon reflex is lost

The triple response of Lewis consists of a red spot, a wheal and a surrounding flare, which depends on an intact axon reflex of sensory nerve endings. In leprosy patches, nerve damage abolishes the flare.

Option by option

A. The central red spot
The red spot is due to local vasodilatation and persists.
B. The central wheal
The wheal results from local capillary permeability and persists.
C. All three components are normal
The flare is characteristically absent in nerve damage.
D. The flare, as the axon reflex is lost (correct)
Correct. Loss of the axon reflex abolishes the flare.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Dermatology question

What is the answer to this Dermatology question?

The best answer is D, The flare, as the axon reflex is lost. The triple response of Lewis consists of a red spot, a wheal and a surrounding flare, which depends on an intact axon reflex of sensory nerve endings.

Why is "The central red spot" not the answer?

The red spot is due to local vasodilatation and persists.

Why is "The central wheal" not the answer?

The wheal results from local capillary permeability and persists.

Why is "All three components are normal" not the answer?

The flare is characteristically absent in nerve damage.

What concept does this question test?

It tests Leprosy: histamine test in Dermatology. In leprosy patches, nerve damage abolishes the flare.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Leprosy: histamine test?

Learn each condition by its primary lesion, site and signature sign. Then use the flashcards and the other Dermatology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.